The present invention relates to a lubrication system, and more particularly to a secondary lubrication system that incorporates a concentrated lubricating oil additive selectively injected into the secondary lubrication system to enable prolonged oil-out operation.
Rotary-wing aircraft power transmission systems incorporate a multitude of gears and bearings which are subject to heat, sliding and surface wear. Such conditions are significantly increased during oil-out operating conditions caused by, for example, ballistic damage, pump failure and system leaks. The primary components of a power transmission system which may be failure points under oil-out conditions include bearings and gears which are constantly oil lubricated under normal conditions using pressurized oil jets or splash oil lubrication methods.
The United States Department of Defense (U.S. DoD) currently imposes a requirement that all rotary-wing aircraft power transmission systems operate for a predetermined period of time in an oil-out condition. The requirement includes the capability to maintain flight operations for 30 to 60 minutes during the oil-out condition, albeit at reduced power levels, sufficient only to sustain level flight operations.
Various emergency or secondary lubrication systems are known and practiced. Lubricating wicks and jets have been provided for lubricating individual components along with a small recirculation system. Air aspirated nozzles have also been utilized for delivering a stream of oil to each individual component. Even through relatively effective, these existing systems have not completely satisfies the U.S. DoD imposed requirements.
Accordingly, it is desirable to provide a secondary or emergency lubrication system which allows a power transmission system to operate for a prolonged time period under oil-out conditions.